JP2022179883A - Method for recycling carbon fiber - Google Patents

Abstract

To provide a method for recycling a carbon fiber that can yield continuous carbon fiber, for example.SOLUTION: A method for recycling a carbon fiber according to the present embodiment includes: a process for preparing a carbon fiber reinforced resin molded product having a carbon fiber reinforced resin containing the carbon fiber and resin; and a process of drawing out the carbon fiber reinforced resin while applying heat treatment to the carbon fiber reinforced resin molded product. A temperature of the heat treatment is above a glass transition temperature of the resin and below a thermal decomposition start temperature, and below a thermal degradation temperature of the carbon fiber.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method of recycling carbon fiber.

Carbon fiber reinforced plastic (CFRP) is a lightweight, highly rigid material that can withstand high-pressure hydrogen. Therefore, it is used in carbon fiber reinforced resin moldings such as hydrogen tanks for fuel cell (FC) vehicles. In addition to tanks, carbon fiber reinforced resin molded products are used in a wide range of fields such as sports/leisure goods and aerospace components. However, the carbon fiber contained in the carbon fiber reinforced resin is expensive, generates a large amount of CO ₂ during production, and is difficult to dispose of, resulting in a high environmental load. Therefore, a method of recovering and recycling carbon fibers from used carbon fiber reinforced resin moldings has been studied.

For example, Patent Literature 1 discloses a method of obtaining the carbon fiber base material as a recycled carbon fiber bundle from a carbon fiber reinforced resin containing a plurality of carbon fiber base materials and a matrix resin. A method for producing a recycled carbon fiber bundle is disclosed, in which a matrix resin is thermally decomposed to obtain a heat-treated product, and the heat-treated product is pulverized to separate the plurality of carbon fiber base materials.

International Publication No. 2018/212016

As disclosed in Patent Literature 1, a method for recovering carbon fibers from carbon fiber reinforced resin moldings has been studied. However, Patent Literature 1 proposes a step of crushing the matrix resin, which makes it impossible to obtain continuous carbon fibers. Therefore, it is not possible to obtain carbon fibers that can be reused for moldings that require continuous carbon fibers.

Further, in Patent Document 1, the matrix resin is thermally decomposed by heating the carbon fiber reinforced resin at a high temperature. However, the carbon fiber may deteriorate due to heating at a high temperature, resulting in a decrease in strength. In addition, when the carbon fiber reinforced resin is heated at a high temperature, the properties such as the solubility of the resin change, which may make it difficult to remove the resin in a subsequent step.

Further, in Patent Document 1, it is proposed to obtain carbon fibers by removing the matrix resin. It is considered possible to reuse the carbon fiber reinforced resin.

Therefore, the present embodiment has been made in view of any of the above problems. For example, one of the objects of the present embodiment is to provide a carbon fiber recycling method capable of obtaining continuous carbon fibers. Further, for example, one of the objects of the present embodiment is to provide a carbon fiber recycling method that can suppress deterioration of carbon fibers and obtain continuous carbon fibers. Further, for example, one of the objects of the present embodiment is to provide a carbon fiber recycling method that can suppress deterioration of carbon fibers and obtain a carbon fiber reinforced resin. Further, for example, one of the purposes of the present embodiment is to provide a carbon fiber recycling method that can obtain a carbon fiber reinforced resin while suppressing deterioration of the resin. Further, for example, one of the objects of the present embodiment is to provide a carbon fiber recycling method that can suppress deterioration of carbon fibers and resin to obtain a carbon fiber reinforced resin.

One aspect of this embodiment is as follows.

(1) A method of recycling carbon fibers, comprising:
A step of preparing a carbon fiber reinforced resin molded product having a carbon fiber reinforced resin containing carbon fibers and a resin, and a step of drawing out the carbon fiber reinforced resin while heat-treating the carbon fiber reinforced resin molded product,
A method in which the temperature of the heat treatment is equal to or higher than the glass transition temperature of the resin and lower than the thermal decomposition initiation temperature and lower than the thermal deterioration temperature of the carbon fiber.
(2) The thermal decomposition starting temperature of the resin is 5% weight loss in the weight change chart of thermogravimetric analysis obtained by raising the temperature of the resin from 30 ° C. to 550 ° C. at 5 ° C./min in a nitrogen atmosphere. The method according to (1), wherein the temperature is
(3) The thermal decomposition starting temperature of the resin is 5% weight loss in the weight change chart of thermogravimetric analysis obtained by raising the temperature of the resin from 30 ° C. to 550 ° C. at 5 ° C./min in the air atmosphere. The method according to (1), wherein the temperature is
(4) The method according to any one of (1) to (3), wherein the heat treatment temperature is less than 400°C.
(5) The method according to any one of (1) to (4), wherein the heat treatment temperature is 360° C. or less.
(6) The method according to any one of (1) to (5), further comprising a step of removing the resin in the withdrawn carbon fiber reinforced resin.
(7) The method according to (6), wherein the step of removing the resin comprises contacting the solution with the carbon fiber reinforced resin.
(8) The method according to (7), wherein the dissolving liquid contains at least one liquid selected from acidic solutions, organic solvents, hydrogen peroxide, and ionic liquids.
(9) The method according to (7) or (8), wherein the dissolving liquid is an acidic solution.
(10) The method according to any one of (6) to (9), further comprising winding the resin-removed carbon fibers.
(11) A step of withdrawing the carbon fiber reinforced resin while performing heat treatment, a step of removing the resin in the withdrawn and conveyed carbon fiber reinforced resin, and a step of winding up the conveyed carbon fiber after removing the resin. and winding the carbon fiber downstream while drawing the carbon fiber reinforced resin upstream.
(12) The method according to any one of (1) to (5), further comprising cutting the drawn carbon fiber reinforced resin.
(13) The method according to any one of (1) to (12), wherein the heat treatment is performed using superheated steam.
(14) The method according to any one of (1) to (13), wherein the resin is a thermosetting resin or a thermoplastic resin.
(15) The method according to any one of (1) to (14), wherein the resin is an epoxy resin.

According to one aspect of the present embodiment, for example, it is possible to provide a carbon fiber recycling method capable of obtaining continuous carbon fibers. In addition, according to one aspect of the present embodiment, for example, it is possible to provide a carbon fiber recycling method that can obtain continuous carbon fibers while suppressing deterioration of the carbon fibers. Further, according to one aspect of the present embodiment, for example, it is possible to provide a carbon fiber recycling method capable of suppressing deterioration of carbon fibers and obtaining a carbon fiber reinforced resin. In addition, according to one aspect of the present embodiment, for example, it is possible to provide a carbon fiber recycling method capable of obtaining a carbon fiber reinforced resin while suppressing deterioration of the resin. In addition, according to one aspect of the present embodiment, for example, it is possible to provide a carbon fiber recycling method that can obtain a carbon fiber reinforced resin while suppressing deterioration of carbon fibers and resin.

It is an example of a flow chart for explaining the method according to the present embodiment. 1 is a schematic cross-sectional view showing a configuration example of a tank 100 as a carbon fiber reinforced resin molded product; FIG. It is a schematic diagram for demonstrating the extraction process under heating in this embodiment. It is a graph showing an example of the thermal properties of an epoxy resin, and is a graph showing a weight change chart (TG curve) of thermogravimetric analysis obtained by heating the resin in a nitrogen atmosphere (horizontal axis: temperature, vertical axis: Weight reduction rate). It is a graph showing an example of the thermal properties of an epoxy resin, and is a graph showing a weight change chart (TG curve) of thermogravimetric analysis obtained by raising the temperature of the resin in an air atmosphere (horizontal axis: temperature, vertical axis: Weight reduction rate). It is a graph showing the thermal properties of carbon fibers, and the strength ratio (tensile It is a graph showing strength/tensile strength before heating). 4 is a graph showing the tensile shear strength ratio (tensile shear strength during heating/tensile shear strength before heating) of an epoxy resin at a given temperature. 7 is a schematic diagram for explaining the configuration of a test piece used in a tensile shear test for measuring the tensile shear strength ratio shown in FIG. 6. FIG. It is the photograph which observed the carbon fiber after immersing carbon fiber reinforced resin in concentrated sulfuric acid and dissolving and removing resin by SEM. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram for demonstrating one aspect|mode of this embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram for demonstrating one aspect|mode of this embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram for demonstrating one aspect|mode of this embodiment.

The present embodiment is a method for recycling carbon fibers, which includes a step of preparing a carbon fiber reinforced resin molded product having a carbon fiber reinforced resin containing carbon fibers and a resin, and a step of heat-treating the carbon fiber reinforced resin molded product. However, the method includes the step of extracting the carbon fiber reinforced resin, and the temperature of the heat treatment is equal to or higher than the glass transition temperature of the resin, lower than the thermal decomposition initiation temperature, and lower than the thermal deterioration temperature of the carbon fiber.

The present embodiment will be described in detail below.

This embodiment is a method of recycling carbon fiber from a carbon fiber reinforced resin molded product.

A carbon fiber reinforced resin molded article has carbon fiber reinforced resin containing carbon fiber and resin. Carbon fibers are continuous carbon fibers. The carbon fiber reinforced resin molded article is not particularly limited, but examples thereof include tanks and the like. Examples of tanks include hydrogen tanks for storing hydrogen. In the following examples, a tank will be mainly described as an example of a carbon fiber reinforced resin molded product, but the present embodiment is not limited to this. The present embodiment relates to a method of recycling carbon fibers, but in the present disclosure, the method of recycling carbon fibers is to manufacture carbon fibers and/or carbon fiber reinforced resins from carbon fiber reinforced resin molded products. It is understood to mean a method.

FIG. 1 shows an example of a flow chart for explaining the method according to this embodiment. As shown in FIG. 1, this embodiment includes at least a molded product preparation step and a drawing step under heating. Each step will be described in detail below.

(Molded product preparation process)
A recycling method according to the present embodiment includes a step of preparing a carbon fiber reinforced resin molded article having a carbon fiber reinforced resin containing carbon fibers and resin.

As described above, the carbon fiber reinforced resin molded article is not particularly limited, and examples thereof include tanks. Examples of carbon fiber reinforced resin molded articles to be prepared include those that were used for various purposes after production and then collected, and defective articles that were produced in the production stage.

FIG. 2 is a cross-sectional view showing a configuration example of the tank 100. As shown in FIG. FIG. 2 shows a cross-sectional view cut along a plane parallel to and passing through the central axis of the tank 100 . The central axis of the tank 100 coincides with the axis passing through the center of the circle of the tank body having a substantially cylindrical shape. Tank 100 can be used, for example, to fill a gas such as compressed hydrogen. For example, the tank 100 is loaded with compressed hydrogen and installed in a fuel cell vehicle to supply hydrogen to the fuel cell.

The tank 100 includes a liner 10 (made of nylon resin), a carbon fiber reinforced resin layer 20 as an outer shell, a valve side mouthpiece 30, an end side mouthpiece 40, and a valve 50. A protective layer 60 is arranged between the liner 10 and the carbon fiber reinforced resin layer 20 . The liner 10 has a hollow shape with a space filled with hydrogen, and has a gas barrier property to seal the internal space so that hydrogen does not leak to the outside.

The carbon fiber reinforced resin layer 20 is a resin layer formed so as to cover the outside of the liner 10 and the protective layer 60 . Carbon fiber reinforced resin layer 20 is formed to cover the outer surface of protective layer 60 . The protective layer 60 is formed so as to cover the inner surface of the carbon fiber reinforced resin layer 20 and also is formed so as to partially cover the mouthpieces 30 and 40 . The carbon fiber reinforced resin layer 20 mainly functions to reinforce the liner 10 (reinforcement layer). Liner 10 is formed to cover the inner surface of protective layer 60 .

In FIG. 2, the valve-side mouthpiece 30 has a substantially cylindrical shape and is inserted and fixed between the liner 10 and the protective layer 60 . A substantially cylindrical opening of the valve-side mouthpiece 30 functions as an opening of the tank 100 . In this embodiment, the valve-side mouthpiece 30 can be made of stainless steel, for example, but it may be made of other metals such as aluminum, or may be made of resin. The valve 50 has a cylindrical portion formed with a male thread, and by being screwed into a female thread formed on the inner surface of the valve side mouthpiece 30, the valve 50 closes the opening of the valve side mouthpiece 30. be done. The end mouthpiece 40 can be made of, for example, aluminum, is assembled with a portion exposed to the outside, and serves to conduct heat inside the tank to the outside.

The carbon fiber reinforced resin layer contains carbon fibers and resin (matrix resin).

Examples of resins include, but are not limited to, phenol resins, urea resins, unsaturated polyester resins, vinyl ester resins, polyimide resins, bismaleimide resins, polyurethane resins, diallyl phthalate resins, epoxy resins, or these resins. mixtures. Epoxy resin is preferable as the resin. As the epoxy resin, those conventionally known in the technical field can be used. Examples of epoxy resins include, but are not limited to, bisphenol A type epoxy resin, bisphenol AD type epoxy resin, bisphenol F type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, glycidyl ester type epoxy resin. etc. The epoxy resin may be linear or branched. One of the resins may be used alone, or two or more of them may be used in combination. Examples of resins include thermoplastic resins and thermosetting resins. Preferably, the resin is a thermoplastic resin.

Carbon fibers can be prepared by methods conventionally known in the art. The carbon fiber may be a material containing carbon as a main component, and examples thereof include carbon fiber made from acrylic, carbon fiber made from pitch, carbon fiber made from polyvinyl alcohol, and the like. Among them, PAN-based carbon fibers produced from polyacrylonitrile fibers are preferred.

A carbon fiber reinforced resin layer can be formed, for example, by a filament winding method. A filament-wound molded product is manufactured by arranging a plurality of carbon fiber bundles as necessary, impregnating them with a matrix resin, and winding them at an appropriate angle while applying tension to a rotating substrate or mold to an appropriate thickness. be able to.

(Extraction process under heating)
The recycling method according to the present embodiment includes a step of extracting the carbon fiber reinforced resin while heat-treating the carbon fiber reinforced resin molded product. Moreover, the temperature of the heat treatment is equal to or higher than the glass transition temperature of the resin and lower than the thermal decomposition initiation temperature, and lower than the thermal deterioration temperature of the carbon fiber.

The heat treatment in the present embodiment can soften the resin in the carbon fiber reinforced resin molded article while suppressing thermal decomposition of the resin and reduction in the strength of the carbon fiber. In the present embodiment, since the carbon fiber reinforced resin molded product is heated to a temperature equal to or higher than the glass transition temperature of the resin, the resin in the carbon fiber reinforced resin molded product is softened. In the present embodiment, the carbon fiber reinforced resin is drawn out after the carbon fiber reinforced resin molded product is heat-treated and the resin is softened. Therefore, the carbon fiber reinforced resin can be easily drawn out from the carbon fiber reinforced resin molded product. Specifically, the carbon fiber reinforced resin can be pulled out from the carbon fiber reinforced resin molded product with a smaller tension. Pulling out with a small tension can suppress breakage and damage of the carbon fibers. On the other hand, in the present embodiment, the carbon fiber reinforced resin molded article is heated at a temperature lower than the thermal decomposition initiation temperature, so thermal decomposition of the resin can be suppressed. By suppressing the thermal decomposition of the resin, it is possible to suppress excessive deformation and carbonization of the resin, and as a result, even when dissolution treatment is performed in a post-process, the resin in the carbon fiber reinforced resin can be easily dissolved. be able to. In addition, by suppressing the thermal decomposition of the resin, it is possible to suppress the decrease in the strength of the resin. It is also possible to apply it and use it for other purposes. Furthermore, in the present embodiment, since the carbon fiber reinforced resin molded product is heated below the thermal degradation temperature of the carbon fibers, the thermal degradation of the carbon fibers can be suppressed, and the reduction in the strength of the carbon fibers can be suppressed.

As described above, in the recycling method according to the present embodiment, the carbon fiber reinforced resin is drawn out while the carbon fiber reinforced resin molded product is being heat-treated.

In the present embodiment, "pull out the carbon fiber reinforced resin" means to pull out the carbon fiber reinforced resin from the carbon fiber reinforced resin molded product in a continuous state, and the carbon fiber reinforced resin is pulled out from the carbon fiber reinforced resin molded product. It also includes the concept of tearing off. In the present embodiment, since the carbon fiber reinforced resin is drawn out while the resin in the carbon fiber reinforced resin molded product is softened by heating, the carbon fiber reinforced resin can be easily drawn out. When pulling out the carbon fiber reinforced resin from the carbon fiber reinforced resin molded product, a blade-shaped jig may be used to separate the carbon fiber reinforced resin. By bringing a blade-shaped jig into contact with the portion (resin portion) between the carbon fiber reinforced resin and the molded product so as to cut the adhesive portion (resin portion) between the molded product and the carbon fiber reinforced resin, The carbon fiber reinforced resin can be easily peeled off.

The method for pulling out the carbon fiber reinforced resin is not particularly limited, and for example, the end of the carbon fiber reinforced resin can be directly or indirectly connected to the take-up roller and pulled out by rotating the roller. can.

Heat treatment can be performed, for example, in a heat treatment chamber. The carbon fiber reinforced resin molded product is heated in a heat treatment chamber to soften the matrix resin of the carbon fiber reinforced resin molded product. The heat treatment chamber may be a heating furnace, or may be a heating apparatus having a space configured so that a heating medium can be introduced and/or discharged.

As a method of extracting the carbon fiber reinforced resin while heat-treating the carbon fiber reinforced resin molded product, for example, as shown in FIG. A method of withdrawing part of the carbon fiber reinforced resin from the heat treatment chamber can be mentioned. The carbon fiber reinforced resin can be transported to the outside, for example, through an outlet provided in a part of the heat treatment chamber. The carbon fiber reinforced resin can be conveyed continuously by, for example, conveying rollers.

In this embodiment, the temperature of the heat treatment is equal to or higher than the glass transition temperature of the resin and lower than the thermal decomposition initiation temperature and lower than the thermal deterioration temperature of the carbon fiber.

In the present embodiment, by heating the carbon fiber reinforced resin molded product to a temperature equal to or higher than the glass transition temperature of the resin, the resin is softened and the carbon fiber reinforced resin can be pulled out with a smaller tension. In addition, since it can be pulled out with a small tension, it is possible to suppress breakage and damage to the carbon fibers. Thermal decomposition of the resin can be suppressed by heating the carbon fiber reinforced resin molded article below the thermal decomposition initiation temperature of the resin. By suppressing the thermal decomposition of the resin, it is possible to suppress excessive deformation and carbonization of the resin. can be dissolved in In addition, by suppressing the thermal decomposition of the resin, it is possible to suppress the decrease in the strength of the resin. cutting, etc.) to use it for other purposes.

The thermal decomposition initiation temperature can be measured using a thermogravimetry device.

In the present embodiment, the thermal decomposition initiation temperature is preferably 5% weight in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30 ° C. to 550 ° C. at 5 ° C./min under a nitrogen atmosphere. It is the temperature that shows the decrease. Preferably, the thermal decomposition starting temperature is the temperature at which the weight decreases by 3% in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30 ° C. to 550 ° C. at 5 ° C./min under a nitrogen atmosphere. be. Preferably, the thermal decomposition starting temperature is the temperature at which the weight decreases by 1% in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30 ° C. to 550 ° C. at 5 ° C./min under a nitrogen atmosphere. be. In general, the thermal decomposition initiation temperature in a nitrogen atmosphere is considered to be the temperature at which decomposition of the main chain and/or side chains of the resin begins.

In the present embodiment, the thermal decomposition initiation temperature is preferably 5% weight in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30 ° C. to 550 ° C. at 5 ° C./min in an air atmosphere. It is the temperature that shows the decrease. Preferably, the thermal decomposition starting temperature is the temperature at which the weight decreases by 3% in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30 ° C. to 550 ° C. at 5 ° C./min in an air atmosphere. be. Preferably, the thermal decomposition starting temperature is the temperature at which the weight decreases by 1% in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30 ° C. to 550 ° C. at 5 ° C./min in an air atmosphere. be. In general, when heating in the air, oxidative decomposition proceeds due to the oxygen contained in the air. Assuming that the weight loss rate is the same, the thermal decomposition initiation temperature measured in the air atmosphere is the temperature measured in the nitrogen atmosphere. lower than the thermal decomposition start temperature.

In the present embodiment, by heating the carbon fiber reinforced resin molded article below the thermal deterioration temperature of the carbon fibers, it is possible to suppress the reduction in the strength of the carbon fibers. The thermal degradation temperature of carbon fibers can be defined as the lowest temperature at which a decrease in tensile strength of 1% or more occurs when the carbon fibers are heat treated in the atmosphere. By measuring the tensile strength of the carbon fiber used in the carbon fiber reinforced resin before and after the heat treatment, the reduction in strength can be calculated.

In one embodiment, the temperature of the heat treatment is preferably 100° C. or higher, preferably 120° C. or higher, preferably 140° C. or higher, preferably 160° C. or higher, preferably 180° C. or higher. , preferably 200° C. or higher. The temperature of the heat treatment is preferably less than 400°C, preferably 390°C or less, preferably 380°C or less, preferably 370°C or less, preferably 360°C or less, preferably 350°C or lower, preferably 340°C or lower, preferably 330°C or lower, preferably 320°C or lower, preferably 310°C or lower, preferably 300°C or lower, preferably 290°C or less, preferably 280° C. or less. When the heat treatment temperature is 100° C. or higher, the resin in the carbon fiber reinforced resin can be effectively softened. When the temperature of the heat treatment is less than 400° C., thermal decomposition of the resin in the carbon fiber reinforced resin can be easily suppressed, and deterioration of the carbon fibers can be easily suppressed. The upper limit and/or lower limit of these numerical ranges can be combined arbitrarily to define a preferred range.

For example, the glass transition temperature of epoxy resin is about 100.degree. C. to 200.degree. C., and the thermal decomposition starting temperature of epoxy resin is about 240.degree. If the resin is heated at a temperature higher than the thermal decomposition initiation temperature, excessive thermal decomposition of the resin occurs and the strength of the resin greatly decreases. In addition, excessive deformation or carbonization of the resin occurs, making it difficult to dissolve and remove the resin with the solution. FIG. 4A shows a weight change chart of thermogravimetric analysis obtained by heating the resin from 30° C. to 550° C. at a rate of 5° C./min under a nitrogen atmosphere for an epoxy resin as an example. In FIG. 4A, the temperature at which the weight decreases by 5% is approximately 350° C., and this temperature can be defined as the thermal decomposition initiation temperature. Further, FIG. 4B shows a weight change chart of thermogravimetric analysis obtained by heating the resin from 30° C. to 550° C. at 5° C./min in an air atmosphere for an epoxy resin as an example. Inflection points are also shown in FIGS. 4A and 4B. In FIG. 4B, the temperature at which the weight decreases by 5% is 340° C., and in this embodiment, this temperature can also be defined as the thermal decomposition initiation temperature. As described above, when heating in the air, oxidative decomposition proceeds due to the oxygen contained in the air, so if the weight loss rate is the same, the thermal decomposition start temperature measured in the air atmosphere is the same as the temperature measured in the nitrogen atmosphere. lower than the thermal decomposition start temperature. Above the thermal decomposition initiation temperature, excessive thermal decomposition of the resin occurs, excessive decomposition of the main chain and/or side chains of the resin occurs, and in some cases carbonization of the resin occurs. When such thermal decomposition occurs, it becomes difficult to dissolve and remove the resin with a solution. In addition, since the strength of the resin is lowered, the carbon fiber reinforced resin itself cannot be reused. On the other hand, in the range above the glass transition temperature and below the thermal decomposition start temperature specified in the present embodiment, the resin can be softened while suppressing thermal decomposition. can easily obtain a continuous carbon fiber reinforced resin. Thermogravimetric analysis is a method of measuring the weight change when the temperature of a substance is changed according to a predetermined program. In the present embodiment, thermogravimetric analysis is performed by, for example, placing about 10 mg of a test piece in a container made of aluminum, alumina or platinum, and raising the temperature at a constant heating rate (5 ° C./min). It can be done by measuring the weight change of.

In the present embodiment, from the viewpoint of more effectively suppressing the thermal decomposition of the resin, the temperature of the heat treatment is preferably 1° C. or more lower than the thermal decomposition initiation temperature, and is 5° C. lower than the thermal decomposition initiation temperature. It is preferably a temperature lower than the thermal decomposition initiation temperature, preferably a temperature lower than the thermal decomposition initiation temperature by 10°C or higher, preferably a temperature lower than the thermal decomposition initiation temperature by 15°C or higher, and lower than the thermal decomposition initiation temperature. The temperature is preferably 20° C. or more, preferably 25° C. or more lower than the thermal decomposition initiation temperature, and preferably 30° C. or more lower than the thermal decomposition initiation temperature.

FIG. 5 is a graph showing the thermal properties of carbon fibers, showing the strength ratio ( Tensile strength after heating/tensile strength before heating). As shown in FIG. 5, it can be seen that the carbon fiber does not lose its strength even when heated at 400.degree. On the other hand, it can be seen that the strength decreases when the carbon fiber is heated at 500° C., which is the temperature of conventional general heat treatment. This is presumably because heat and oxygen caused oxidative deterioration of the carbon fibers. Generally, it is considered that the thermal decomposition starting temperature of the resin is often lower than the thermal degradation temperature of the carbon fiber.

FIG. 6 is a graph showing the tensile shear strength ratio of a resin (epoxy resin, see FIG. 4) at a given temperature. Specifically, FIG. 6 shows the tensile shear strength ratio (tensile shear strength during heating/tensile shear strength before heating (23 ° C. (intensity at ), vertical axis, ● mark). A dotted line from 250° C. to 350° C. indicates a virtual curve. As shown in FIG. 7, the tensile shear strength refers to the force applied when two plates are bonded with a resin and the bonding joint is broken by the shear stress, which is a load that causes the adherends to shift in opposite directions. Strength. As shown in FIG. 6, it can be seen that the higher the heating temperature of the resin, the lower the tensile shear strength. When the tensile shear strength is lowered, the carbon fiber reinforced resin can be easily pulled out. For example, when the heating temperature is 150 ° C., the tensile shear strength ratio is 0.2 or less, and the tensile shear strength during heating is 20% or less compared to the tensile shear strength before heating, which is a smaller force. It can be seen that the carbon fiber reinforced resin can be extracted at In the present embodiment, the temperature of the heat treatment is preferably a temperature at which the tensile shear strength ratio is 20% or less, preferably a temperature at which the tensile shear strength ratio is 15% or less, and the tensile shear strength ratio is The temperature is preferably 10% or less, and the temperature is preferably 5% or less of the tensile shear strength ratio.

In this embodiment, the carbon fiber reinforced resin molded product is not usually crushed or pulverized. Only the cylindrical portion of the tank may be used as the carbon fiber reinforced resin molded product. Metal parts and the like in the carbon fiber reinforced resin molded article may be removed before the heating process or after the heating process.

A heating method is not particularly limited. As a heating method, for example, heating in the atmosphere can be mentioned. The heat treatment in air can be easily performed and is advantageous in terms of cost. In particular, the present embodiment is effective because deterioration of carbon fibers can be suppressed even in the presence of oxygen such as air. In addition, the heat treatment can be performed using superheated steam. By using superheated steam, the proportion of oxygen-containing air in the treatment atmosphere can be reduced, so that decomposition and damage to the carbon fibers can be effectively suppressed. For example, the heat treatment can be performed by introducing superheated steam at normal pressure into the reaction vessel at normal pressure. In addition, the heat treatment may be performed in an inert atmosphere such as nitrogen, although it is not particularly limited. The heat treatment may be performed while supplying heated superheated steam and/or an inert gas (such as nitrogen) into the heat treatment chamber.

In the carbon fiber recycling method according to the present embodiment, the carbon fiber reinforced resin pulled out in the heating step is kept in a bundle shape by the carbon fiber and the matrix resin. As described above, in the present embodiment, the carbon fiber reinforced resin can be reused as it is because the decrease in the strength of the resin and the carbon fiber is suppressed. In addition, depending on the case, the obtained carbon fiber reinforced resin may be subjected to desired processing and reused. Processing includes, for example, cutting into desired dimensions. For example, a sheet-like product can be produced by appropriately mixing a cut carbon fiber reinforced resin with a binder resin or the like and solidifying the mixture.

(Removal process)
The recycling method according to the present embodiment may include a step of obtaining carbon fibers by removing the resin in the carbon fiber reinforced resin. A method for removing the resin in the carbon fiber reinforced resin is not particularly limited, but preferably includes dissolving and removing with a solution. Deterioration of the carbon fibers can be suppressed by dissolving and removing the carbon fibers with the dissolving liquid.

A dissolution removal step using a dissolution liquid will be described below as an example of the step of removing the resin.

The dissolution removal step is a step of dissolving and removing the resin in the drawn out carbon fiber reinforced resin with a dissolving liquid.

In one embodiment, the resin in the extracted carbon fiber reinforced resin is removed by a dissolution removal step. The resin can be dissolved and removed by bringing the carbon fiber reinforced resin into contact with the solution. Dissolution and removal can avoid thermal stress and suppress deterioration of the carbon fibers. Specifically, removal by solution causes less degradation of the carbon fibers than removal by pyrolysis. In addition, in the present embodiment, since excessive deformation and carbonization of the resin are suppressed in the drawing process under heating, which is the previous process, the resin in the carbon fiber reinforced resin can be efficiently dissolved.

The dissolution of the resin is performed using a dissolving liquid capable of dissolving the resin in the carbon fiber reinforced resin. The dissolving liquid is not particularly limited as long as it can dissolve the resin, and includes, for example, at least one liquid selected from acidic solutions, organic solvents, hydrogen peroxide water, and ionic liquids. . These liquids can dissolve or swell the resin, and can efficiently remove the resin. The dissolution liquid may be used singly or in combination of two or more.

Acidic solutions include, for example, phosphoric acid and sulfuric acid. Examples of the acidic solution include a solution containing sulfuric acid (eg, a concentration of 90% by mass or more) as described in JP-A-2020-37638, and phosphoric acid as described in JP-A-2020-50704. and the like. The acidic component may be used singly or in combination of two or more.

Examples of organic solvents include aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, amide solvents, ester solvents, and the like. An organic solvent may be used individually by 1 type, and may be used in combination of 2 or more type. Examples of aliphatic hydrocarbon solvents include pentane, hexane, heptane, octane, and the like. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, and the like. Examples of organic solvents containing two or more components include petroleum benzine and ligroin. The organic solvent may contain a decomposition catalyst. as a decomposition catalyst. Examples thereof include alkali metal compounds as described in JP-A-2020-45407.

Ionic liquids include, for example, ionic liquids containing at least one cation selected from imidazolium-based, pyridinium-based, pyrrolidinium-based, quaternary ammonium-based, and quaternary phosphonium-based cations. One type of ionic liquid may be used alone, or two or more types may be used in combination.

FIG. 8 is a SEM photograph of carbon fibers obtained by immersing a carbon fiber reinforced resin in concentrated sulfuric acid to dissolve and remove the resin. The temperature of concentrated sulfuric acid can be, for example, 100-300°C. As shown in FIG. 8, it can be seen that the dissolving solution can efficiently remove the resin from the carbon fiber reinforced resin. Further, no substantial decrease in strength was observed in the carbon fibers after removing the resin with the dissolving solution.

Dissolving and removing the resin is performed by bringing the solution into contact with the carbon fiber reinforced resin. The method of bringing the solution into contact with the carbon fiber reinforced resin is not particularly limited, but examples thereof include dipping, die coating, bar coating, roll coating, gravure coating, and the like. Among these, the dipping method is preferred. Specifically, the dissolving liquid can be brought into contact with the carbon fibers by conveying the carbon fiber reinforced resin with rollers so as to be immersed in the dissolving liquid placed in a bath. In one embodiment, the pulled-out carbon fiber reinforced resin can be immersed in the solution while being conveyed by a conveying roller or the like.

The degree of dissolution of the resin in the dissolution removal step can be adjusted by the type of solution, treatment temperature, treatment time, or the like. The treatment time can be adjusted, for example, by the conveying speed of the carbon fiber reinforced resin. The treatment time is not particularly limited, and can be appropriately set according to the type of solution, resin, and the like.

The temperature of the solution (liquid temperature) can be appropriately set in consideration of the degree of removal by dissolution. The temperature of the solution (liquid temperature) is, for example, 20° C. or higher, 40° C. or higher, 60° C. or higher, 80° C. or higher, or, for example, 300° C. or lower, and 250° C. or lower. 200° C. or lower, 150° C. or lower, and 100° C. or lower.

Dissolution and removal of the resin may be performed by injecting the solution onto the carbon fiber reinforced resin. That is, by applying injection pressure to the solution to bring it into contact with the carbon fiber reinforced resin, the injection pressure can be used to remove the resin in the carbon fiber reinforced resin. There are no particular restrictions on the injection device used to inject the dissolving liquid, and for example, a high-pressure washing device or the like can be used.

The nozzle pressure when spraying the solution is preferably 1 MPa or higher, preferably 5 MPa or higher, preferably 8 MPa or higher, and preferably 10 MPa or higher. With the above pressure, the resin can be efficiently removed from the carbon fiber reinforced resin. Further, the nozzle pressure is preferably 30 MPa or less, preferably 25 MPa or less, preferably 22 MPa or less, preferably 20 MPa or less. With the above pressure, it is possible to effectively suppress the carbon fibers from being damaged by the solution. The distance between the nozzle and the carbon fiber reinforced resin to be sprayed when spraying the solution is preferably 10 to 200 cm, more preferably 30 to 100 cm.

Dissolution and removal of the resin may be performed by combining immersion in the solution and injection of the solution.

(Step of applying sizing agent)
The recycling method according to this embodiment may include a step of attaching a sizing agent to the carbon fibers obtained by removing the resin.

Substantially all of the resin has been removed from the carbon fibers after the removal step, and the bundles of the carbon fibers are unraveled to form single fibers. By adding a sizing agent to the carbon fibers, the carbon fiber bundle can be easily wound up as a bobbin, and the occurrence of fluffing of the carbon fibers and entanglement of the single fibers can be suppressed.

Examples of sizing agents include, but are not limited to, epoxy resins, urethane resins, vinyl ester resins, polyamide resins, nylon resins, polyolefin resins (polyethylene and polypropylene), polyester resins, phenol resins, and mixtures thereof. is mentioned. Among these, epoxy resin, urethane resin, vinyl ester resin, or polyolefin resin is preferable, and epoxy resin is more preferable. By using the epoxy resin as the sizing agent, the adhesion between the carbon fibers and the epoxy resin can be improved. The sizing agents may be used singly or in combination of two or more.

The sizing agent is applied to the carbon fibers by bringing the sizing agent into contact with the carbon fibers. The method of applying the sizing agent is not particularly limited, and examples thereof include dipping, die coating, bar coating, roll coating, gravure coating, and the like. Among these, the dipping method is preferable. Specifically, the sizing agent can be applied to the carbon fibers by transporting the carbon fibers with rollers so that they are immersed in the sizing agent placed in a sizing bath. The sizing agent is preferably dispersed or dissolved in water or an organic solvent such as acetone and used as a dispersion or solution. From the viewpoint of enhancing the dispersibility of the sizing agent and improving the liquid stability, a surfactant may be appropriately added to the dispersion or solution.

The amount of the sizing agent attached to the carbon fibers is, for example, 0.1 to 10 parts by mass when the total amount of the carbon fibers and the sizing agent is 100 parts by mass. If the adhesion amount is within this range, appropriate convergence of the carbon fibers can be obtained, and sufficient abrasion resistance of the carbon fibers can be obtained, thereby suppressing the generation of fluff due to mechanical friction or the like.

(Winding process)
The recycling method according to the present embodiment may include a step of winding the resin-removed carbon fibers obtained in the removing step. The step of winding the carbon fibers is performed after the removing step, and when the step of applying the sizing agent is included, it is preferably performed after the step of applying the sizing agent.

Winding can be performed, for example, using a winding roller. A driving device is attached to the winding roller to provide a driving force for winding the carbon fibers. Also, some of the guide rollers may be attached with a driving device for rotating the guide rollers. It is desirable that the winding tension, that is, the tension applied to the carbon fibers, is smaller. By setting the winding tension within an appropriate range, it is possible to prevent the carbon fiber from breaking and winding misalignment, and as a result, a longer continuous fiber can be obtained.

One embodiment includes a step of drawing out the carbon fiber reinforced resin while performing heat treatment, a step of removing the resin in the drawn out and conveyed carbon fiber reinforced resin, and a step of winding the conveyed carbon fiber after removing the resin. The carbon fiber is wound downstream while pulling out the carbon fiber reinforced resin upstream. That is, in one embodiment, while performing the step of pulling out the carbon fiber reinforced resin under heating in the upstream, the step of winding the carbon fiber in the downstream is performed, and the removing step is performed between the upstream pulling step and the downstream winding step. and optionally a step of applying a sizing agent. Further, in one embodiment, while performing the step of drawing the carbon fiber reinforced resin under heating in the upstream, the step of winding the carbon fiber is performed in the downstream, and the carbon fiber is dissolved and removed between the upstream drawing step and the downstream winding step. A step and optionally a sizing agent application step are performed. In such an embodiment, the dissolution removal step can be performed immediately after the drawing step under heating, and the carbon fiber reinforced resin can be brought into contact with the solution while the temperature is high. Resin can be removed efficiently. Specifically, a part of the carbon fiber reinforced resin (preferably the end) is taken out from the carbon fiber reinforced resin molded product, and the part of the taken out carbon fiber reinforced resin is directly or indirectly Tension is applied to the carbon fiber reinforced resin by a winding machine, and the carbon fiber reinforced resin is pulled out in a continuous fiber state. The extracted carbon fiber reinforced resin is removed with a solution. Then, the carbon fibers obtained by removing the resin are wound up by a winder.

In the carbon fiber recycling method according to the present embodiment having the steps described above, carbon fibers suitable for reuse can be efficiently obtained.

A specific example of this embodiment will be described below with reference to FIGS. In the example of this embodiment shown in FIGS. 9 to 11 below, the molded product preparation step and the sizing agent application step are not shown, but the carbon fiber reinforced resin molded product subjected to the treatment steps of each embodiment is , prepared by the molded product preparation step. In addition, in each embodiment, a step of applying a sizing agent may optionally be performed.

FIG. 9 is a schematic diagram for explaining one aspect of the present embodiment. In the embodiment shown in FIG. 9, the drawing step under heating is performed upstream, followed by the removal step (immersion in the solution) and then the winding step downstream. Specifically, the carbon fiber reinforced resin molded article 200 is housed in an apparatus 210 capable of heat treatment such as a heat treatment chamber, and the carbon fiber reinforced resin is pulled out while performing heat treatment (heated pulling step). In the heat treatment chamber, a tank is mounted on a rotatable bearing, and the carbon fiber reinforced resin is pulled out from the tank while being heated. Next, the extracted carbon fiber reinforced resin is immersed in the solution 230 (removal step). Next, the carbon fiber from which the resin has been removed is wound up (winding step). The method of conveying the carbon fiber reinforced resin or carbon fibers between steps is not particularly limited, and can be carried out using, for example, guide rollers, take-up rollers, and mandrel rollers. Also, although not shown, it is preferable to perform the sizing agent applying step after the removing step and before the winding step. Further, a step of drying the carbon fibers after the removal step or the carbon fibers after the sizing agent application step may be performed.

FIG. 10 is a schematic diagram for explaining one aspect of the present embodiment. In FIG. 10, the removing step is performed by injecting the dissolving liquid onto the pulled out carbon fiber reinforced resin. Specifically, in FIG. 10, a dissolving liquid 250 is jetted from a nozzle 240 connected to a jetting device (not shown) to the carbon fiber reinforced resin pulled out to remove the resin from the carbon fibers. By moving the nozzle for injecting the solution or the carbon fiber reinforced resin, the solution can be brought into contact with the entire carbon fiber reinforced resin. A plurality of nozzles may be provided. Also, although not shown, it is preferable to perform the sizing agent applying step after the removing step and before the winding step. Further, a step of drying the carbon fibers after the removal step or the carbon fibers after the sizing agent application step may be performed.

FIG. 11 is a schematic diagram for explaining one aspect of the present embodiment. In FIG. 11, the removal step is performed by a combination of immersion in the dissolving liquid and jetting of the dissolving liquid. Specifically, in FIG. 11, after the extracted carbon fiber reinforced resin is immersed in a solution 230, the carbon fiber reinforced resin is subsequently dissolved from a nozzle 240 connected to an injection device (not shown). By injecting the liquid 250, the resin is removed from the carbon fibers. By combining the immersion in the solution and the injection of the solution, the resin can be removed more efficiently. Also, although not shown, it is preferable to perform the sizing agent applying step after the removing step and before the winding step. Further, a step of drying the carbon fibers after the removal step or the carbon fibers after the sizing agent application step may be performed.

According to the carbon fiber recycling method of the present embodiment described above, it is possible to efficiently obtain high-quality carbon fibers suitable for reuse. The obtained carbon fibers are applicable to a wide range of uses.

The upper and/or lower limits of the numerical ranges described herein can be combined arbitrarily to define a preferred range. For example, a preferred range can be defined by arbitrarily combining the upper and lower limits of the numerical range, a preferred range can be defined by arbitrarily combining the upper limits of the numerical range, and the lower limit of the numerical range Any combination of values can be used to define a preferred range.

Throughout this specification, any reference to "one embodiment," "an (a) embodiment," or "an embodiment" refers to a specific feature, structure, or characteristic described with respect to that embodiment. is meant to be included in at least one embodiment. Thus, the phrases quoted or variations thereof, appearing throughout this specification are not necessarily all referring to the same embodiment.

Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope of the present disclosure, they are included in the present disclosure. It is.

REFERENCE SIGNS LIST 10 liner 20 carbon fiber reinforced resin layer 30 valve side mouthpiece 40 end side mouthpiece 50 valve 60 protective layer 100 tank 210 heat treatment device (heat treatment chamber)
220 carbon fiber reinforced resin molded product 230 solution 240 nozzle 250 solution

Claims (15)

A method of recycling carbon fiber comprising:
A step of preparing a carbon fiber reinforced resin molded product having a carbon fiber reinforced resin containing carbon fibers and a resin, and a step of drawing out the carbon fiber reinforced resin while heat-treating the carbon fiber reinforced resin molded product,
A method in which the temperature of the heat treatment is equal to or higher than the glass transition temperature of the resin and lower than the thermal decomposition initiation temperature and lower than the thermal deterioration temperature of the carbon fiber. The temperature at which the thermal decomposition of the resin starts is the temperature at which the weight decreases by 5% in the weight change chart of thermogravimetric analysis obtained by heating the resin from 30° C. to 550° C. at 5° C./min under a nitrogen atmosphere. 2. The method of claim 1, wherein there is The temperature at which the thermal decomposition of the resin starts is the temperature at which the weight decreases by 5% in the weight change chart of thermogravimetric analysis obtained by raising the temperature of the resin from 30°C to 550°C at 5°C/min in an air atmosphere. 2. The method of claim 1, wherein there is The method according to any one of claims 1 to 3, wherein the heat treatment temperature is less than 400°C. The method according to any one of claims 1 to 4, wherein the heat treatment temperature is 360°C or less. The method according to any one of claims 1 to 5, further comprising removing resin in the withdrawn carbon fiber reinforced resin. 7. The method of claim 6, wherein removing the resin comprises contacting the solution with the carbon fiber reinforced resin. 8. The method according to claim 7, wherein the dissolving liquid contains at least one liquid selected from acidic solutions, organic solvents, hydrogen peroxide water, and ionic liquids. 9. The method according to claim 7 or 8, wherein the dissolving liquid is an acidic solution. The method of any one of claims 6 to 9, further comprising winding the resin-removed carbon fibers. It includes a step of drawing out the carbon fiber reinforced resin while applying heat treatment, a step of removing the resin in the drawn out and conveyed carbon fiber reinforced resin, and a step of winding up the conveyed carbon fiber after removing the resin. 11. The method of claim 10, wherein the carbon fiber is wound downstream while the carbon fiber reinforced resin is drawn upstream. The method according to any one of claims 1 to 5, further comprising cutting the withdrawn carbon fiber reinforced resin. The method according to any one of claims 1 to 12, wherein the heat treatment is performed using superheated steam. A method according to any one of claims 1 to 13, wherein the resin is a thermosetting resin or a thermoplastic resin. The method of any one of claims 1-14, wherein the resin is an epoxy resin.

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